Valve timing control for internal combustion engines

Abstract

An engine intake system includes a combustion chamber, a first intake port opening to the combustion chamber, and a second intake port opening to the combustion chamber. A shut-off valve is provided for blocking intake gas flow to the combustion chamber through the second intake port in a first engine operating region wherein engine load is relatively small, and allowing the intake gas to flow to the combustion chamber through the second intake port in a second engine operating region wherein the engine load is relatively large. A first valve actuating mechanism is provided for opening the first intake valve at a first timing, and a second valve actuating mechanism is provided for opening the second intake valve at a second timing. A valve timing changing device is provided for changing the first timing with respect to the second timing so that the first intake valve is closed later than the second intake valve in the second engine operating region, and so that the first intake valve is closed at least in a certain engine operating zone in the first engine operating region at a timing which is more advanced than the timing at which the first intake valve is closed in the second engine operating region.